The exhaust emission of diesel engines contains particulate matter (hereinafter, referred to as “PM”), nitride oxide (hereinafter, referred to as “NOx”), or the like. An exhaust emission control device that prevents the particulate matter from being released into the air so as to prevent the air pollution has been developed heretofore. The exhaust emission control device includes, as the constituent elements, a diesel particulate filter (hereinafter, referred to as a “DPF”) for collecting the PM, a diesel oxidation catalyst (hereinafter referred to as “DOC”) for removing the NOx, a decomposition reactor tube (hereinafter referred to as “DRT”), and a selective catalytic reduction (hereinafter referred to as “SCR”). By combining the constituent elements, a desired exhaust emission control device is constituted.
The diesel engine is mounted on various types of vehicles; however, recently, there has been a high demand for exhaust emission control processing, and thus the SCR is employed also in a passenger car, a truck, a crawler construction machine, or the like. Since the urea water is used in the exhaust emission control processing by the SCR, a urea water tank, in which the urea water is stored, is additionally provided on a vehicle (for example, see Patent Documents 1 and 2).
In general, a rough terrain crane includes a carrier device that is capable of four-wheel driving and four-wheel steering, and exhibits excellent small-radius turning performance and rough terrain traveling performance. The rough terrain crane includes a single driver seat, has special performance that enables an operator on the driver seat to drive a vehicle and to perform an operation of a crane. The rough terrain crane is manufactured from compact design for exhibiting such special performance (merit) in which the entire length of the vehicle body is set to be short, an engine is disposed on the rear side of the vehicle body, and a crane operation is controlled by hydraulic pressure.
In a case where the exhaust emission control device is mounted on the rough terrain crane, the entire length and the entire width of the vehicle body must avoid an increase in size, a wide range of view and high visibility need to be secured when an operator performs the crane operation and vehicle driving on a single driving seat. Specifically, the DOC, the DRT, and the SCR are laid out such that the exhaust emission control device does not overhang from an end portion of the vehicle body, a blind spot is not generated to the operator, and the exhaust emission control device does not interfere with the driving seat, a counterweight, or the like during the crane operation and crane slewing (for example, see Patent Document 3).
However, in a large rough terrain crane, a front axle or a rear axle has a multi-axle structure, and a structure with a premise of attaching and detaching an outrigger and a boom to and from a vehicle-body frame is employed in some cases. The main reason for the front axle or the rear axle to have the multi-axis structure is to reduce the entirety of axle load to a certain load or lower. In addition, the reason for the structure with the premise of attaching and detaching the outrigger and the boom to and from the vehicle-body frame is employed is to be in accordance with the legislation of a country or a region where the large rough terrain crane is used. In other words, in some countries or regions, strict weight limit (axle load limit) is imposed on a vehicle traveling on a public road. Therefore, when the large rough terrain crane runs on a public road, the vehicle body, the outrigger, and the boom must be individually transported on a trailer in some cases (Request 1).
The urea water contained in the urea water tank selectively reduces the NOx in the exhaust gas; however, the urea water has properties of being frozen in a low-temperature environment and having degraded product quality in a high-temperature environment. Therefore, in a case where the rough terrain crane is used in a cold region, the urea water needs to avoid being frozen. In addition, also even in a case where the urea water is used in a high-temperature environment, the temperature of the urea water needs to be maintained to be a certain degree (preferably, 52° C. or lower) (Request 2).
If the urea water tank is disposed in any position around a vehicle frame without being in accordance with the requests, various problems arise in that piping, through which the urea water is supplied, becomes unnecessarily long, it is difficult to perform filling work of the urea water to the urea water tank, the urea water is frozen due to an environmental temperature, it is likely to degrade the product quality, and the like. Therefore, special measures are required for the layout of the urea water.